Hundreds of batteries are usually utilized by the battery module of a large electric vehicle, in series or in parallel. In most assembling methods, since it is hard to accurately lock every electrode contacts, a risk of loosening always exists in this type of the battery module. However, when the electric vehicle is moving, the batteries are continuously affected by the continuous vibration of the electric vehicle. That is, when the electric vehicle is operated in a long-time operation, the electrode contacts may be loosened, thereby causing high voltage arcs or sparks. Therefore, there is a need of providing a locking confirmation device to ensure the safety of the battery module.